Joining Dissimilar Materials Using an Epoxy Resin Composition

ABSTRACT

An epoxy resin composition is disclosed for joining dissimilar materials. The identified epoxy resin compositions can fee used to seal metallic and non-metallic components of a capacitor. Specifically the epoxy resin composition can be applied to joints between a non-metallic capacitor bushing and a metallic tank cover and metallic terminal cap. Once the epoxy resin composition is cored, it can provide a seal that can withstand the stresses and environmental conditions to which a capacitor is subjected.

RELATED APPLICATIONS

The present application is a divisional application of and claimspriority under 35 U.S.C. §121 to U.S. patent application Ser. No.14/075,350, titled “Joining Dissimilar Materials Using an Epoxy ResinComposition,” and filed Nov. 8, 2013. The entire content of theforegoing application is hereby incorporated herein by reference.

TECHNICAL FIELD

Embodiments described herein relate generally to joining dissimilarmaterials, such as metallic and non-metallic materials, using an epoxyresin composition.

BACKGROUND

Joining dissimilar materials, such as metallic and non-metallicmaterials, often presents a variety of technical challenges. Not onlyare dissimilar materials resistant to many types of conventional joiningmethods, even joints that are formed may not be able to withstandsubstantial stress or harsh environmental conditions. These challengesare particularly true for electrical equipment that is placed outdoors,however, harsh environmental factors such as high temperatures can alsobe present in indoor environments. For example, in the case of capacitortanks, there is a need to join non-metallic capacitor bushings tometallic terminal caps and metallic tank covers. Capacitor bushingsserve several functions. The primary function of the bushing is toisolate electrical leads, which may be at thousands of volts of electricpotential, from the metal body of the capacitor tank and from eachother. The capacitor hushing is also used io isolate the contents on theinside of the capacitor from the outside environment. It is necessary toprotect the internal capacitor components from contact with, theexterior environment since contamination by moisture or dust may degradethe dielectric capacitor fluid and lead to capacitor failure. Also, thecapacitor bushing seals the dielectric fluid inside the capacitor andprevents it from escaping to the environment.

Currently, there are several different approaches that can be used tojoin these metallic and non-metallic surfaces. One example is soldering.Soldering the capacitor bushings typically involves a complicatedprocedure wherein two coats of a thick silver-based painted film areapplied to the capacitor bashing in a carefully controlled process. Thecoats of paint are dried and then the capacitor hushing is fired at hightemperatures under carefully controlled conditions. After the firingprocess, the capacitor bushing can be soldered to metallic components.The soldering process can be complex, labor-intensive and expensive.

An alternative approach to joining metallic and non-metallic surfaces isto use mechanical components and fasteners. However, mechanicalfastening requires additional components which add expense andcomplexity to the capacitor tank and mechanical fasteners may provideinsufficient joint strength for some applications and may lose sealingintegrity under mechanical stress over the life of the capacitor as itis exposed to harsh environmental conditions.

Accordingly, there is a need for an improved method for joiningdissimilar materials such as the metallic and non-metallic componentsused to manufacture capacitor tanks. Specifically, there is a need foran improved technique for joining metallic and non-metallic componentsthat is a less expensive and simpler process and thai produces astronger joint with more reliable sealing properties during the life ofthe capacitor.

SUMMARY

In general, in one aspect, the disclosure relates to a novel applicationof an epoxy resin composition for joining dissimilar materials.Specifically, in one embodiment, the disclosure relates to a method forforming a cured seal between an insulating material and a metalliccomponent. The example method includes applying an epoxy resincomposition to a portion of one or both of the insulating material andthe metallic component. The insulating material and the metalliccomponent are joined such that the epoxy resin composition forms a sealbetween the insulating material and the metallic component. The seal isthen cured to form the cured seal. The insulating material can compriseone or more of glass, ceramic, epoxy, glazed material, or otherpolymers. The epoxy resin composition can comprise a phenol novoiacepoxy, a bisphenol A epoxy, or a combination thereof, and a caringagent. In the example of a capacitor, once the seal is cured and thecapacitor is completely assembled, the cured seal can be exposed to oneor more aromatic compounds that are placed within the capacitor.

In another aspect, the disclosure can generally relate to an apparatusthat includes an epoxy resin composition that joins two dissimilarmaterials. Specifically, the apparatus can include an insulatingmaterial, a metallic component, and a cured seal between the insulatingmaterial and the metallic component. The cured seal can comprise anepoxy resin composition that includes a phenol novoiac epoxy, abisphenol A epoxy, or a combination thereof, and a curing agent. Theinsulating material can comprise one or more of glass, ceramic, epoxy,glazed material, or other polymers. In the example of a capacitor, theepoxy resin composition is cured to form the cured seal between acapacitor bushing made of an insulating material and a metallic coverand a metallic terminal cap. Once the capacitor is assembled, the curedseal can be exposed to one or more aromatic compounds that are placedwithin the capacitor.

In yet another aspect, the disclosure can relate to a method for forminga cured seal between an Insulating material and a metallic component.The example method includes applying a first part of a composition tothe insulating material and applying a second part of the composition tothe metallic component The insulating material and the metalliccomponent are joined such that the first part and the second part of thecomposition are combined and form an epoxy resin composition between theinsulating material and the metallic component. The epoxy resincomposition is then cured to form a cured seal. The insulating materialcan comprise one or more of glass, ceramic, epoxy, glazed material, orother polymers. The epoxy resin composition can comprise a phenolnovolac epoxy, a bisphenol A epoxy, or a combination thereof, and acuring agent. In the example of a capacitor, once the epoxy resincomposition is cured and the capacitor is completely assembled, thecured seal can be exposed to one or more aromatic compounds that areplaced within the capacitor.

These and other aspects, objects, features, and embodiments will beapparent from the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate duly example embodiments of joining dissimilarmaterials using an epoxy resin composition and are therefore not to beconsidered limiting of its scope. The elements and features shown in thedrawings are not necessarily to scale, emphasis instead being placedupon clearly illustrating the principles of the example embodiments.Additionally, certain dimensions or positionings may be exaggerated tohelp visually convey such principles. In the drawings, referencenumerals designate like or corresponding, but not necessarily identical,elements.

FIG. 1 shows a perspective view of a capacitor partially cut away inaccordance with certain example embodiments.

FIG. 2 shows a perspective view of a capacitor bushing partially cutaway in accordance with certain example embodiments.

FIG. 3 shows an exploded view of a capacitor bushing, tank top, metalcasing, terminal cap, and O-ring in accordance with certain exampleembodiments.

FIG. 4 shows an example method for assembling a capacitor in accordancewith certain example embodiments.

FIG. 5 is a representation of an adhesive bonding a ceramic material anda metallic material in accordance with certain example embodiments.

FIG. 6 is a representation of a metallic surface in accordance withcertain example embodiments. The illustration on the left displays thechemical composition of the layers of a metallic surface before removalof contaminants. The illustration on the right represents the chemicalinteraction of the layers of a metallic surface after removal ofcontaminants.

FIG. 7 shows the assessment of the hardness of the cured seal inaccordance with certain example embodiments before and after exposure tothe aromatic dielectric fluid.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The example embodiments discussed herein are directed to systems,apparatuses, and methods for joining dissimilar materials. One exampleembodiment described herein involves joining metallic and non-metalliccomponents of a capacitor using an epoxy resin composition. However, thenovel application of the disclosed epoxy resin compositions can also beapplied to other types of devices where there is a need to joindissimilar materials. For example, the disclosed epoxy resincompositions can also be used to join dissimilar materials found inother electrical components such as fuses, switchgear, regulators, andtransformers. Thus, the novel application of the disclosed epoxy resincompositions is not limited to the capacitor example provided herein.

The terms “joint” and “cured seal” are used interchangeably herein andone term should not be interpreted as excluding the other, rather, theterms should be given their broadest reasonable Interpretation. The term“insulating material” as used herein is one type of non-metallicmaterial that includes a number of non-metallic materials, but it shouldbe understood that certain non-metallic materials are not effectiveinsulators.

Referring now to the example of the capacitor tank. FIG. 1 shows acapacitor 19 comprised of one or more capacitor windings 10 in a casing20, The easing 20 is filled with a dielectric fluid, Taps 17 and 18 fromcapacitor windings 10 are joined together electrically to leads, notshown, passing through capacitor bushings 40 and terminal caps 42. Taps17 and 18 may be eliminated in some methods of capacitor constructionand the electrical leads may be connected directly to the capacitorwindings 10. The example capacitor 19 of FIG. 1 may comply with one ormore standards as set forth for example by the InternationalEleetrotechnical Commission (IEC) or the Institute of Electrical andElectronics Engineers (IEEE), such as the requirements in IEC60871-1:2005, Section 12—Sealing Test and/or IEEE 18:2012, Section7.2.3—Leak Test.

Capacitor windings 10 typically include a pair of spaced, metal foilelectrodes and intermediate polypropylene film layers so that pairs ofpolypropylene film layers are found between foil electrode layersthroughout the windings as is well known in the art. Taps 17 and 18 areinserted into the capacitor windings 10 to lie adjacent to the electrodelayers to serve as electrical connections for the electrodes. Asreferenced above, alternate embodiments of the capacitor can beconstructed with extended metal layer electrodes connecting toelectrical leads which eliminate the need for separate taps. Electricalleads (not shown) connecting taps 17 and 18 to external electricalconnections at terminal caps 42 are electrically insulated from thecasing 20 of capacitor 19. Casing 20 and tank cover 44 are typicallyfabricated from a durable metal material siteh as stainless steel,however, other durable non-metallic materials could be used as well. Theterminal caps 42 are typically manufactured from one or more metallicmaterials. For example, in one embodiment, the terminal caps 42 can bemade with brass that is plated with tin.

The capacitor windings 10 are also typically immersed in a dielectricfluid such as, for example, mixtures of one or more of mono benzyltoluene, diphenyl ethane, and dibenxyl toluene. The dielectric fluidtypically comprises one or more aromatic fluids which can have corrosiveeffects on certain materials. Typically, water vapor is removed from thedielectric fluid and the components of the capacitor windings 10 as partof the assembly of the capacitor 19.

In order to maintain capacitor 19 and the dielectric fluid free of waterand other impurities, the capacitor 19 must be sealed. The capacitorseals must be able to withstand constant exposure to an environmentwhich includes prolonged exposure to sunlight, extreme temperaturevariations, and exposure to the elements. In general, the capacitorseals must withstand conditions that exist at the top of utility polesor in electrical substations subjected to all types of geographicalconditions and meteorological conditions found throughout the world. Thecapacitor seals are generally expected to be capable of lasting for auseful life of approximately thirty years.

Sealing capacitor 19 is difficult because capacitor bushing 40 istypically comprised of ceramic, epoxy or another insulating material.Insulating material is not readily joined to metal parts such as themetal easing 20 and terminal cap 42. As shown in FIGS. 2 and 3, thecapacitor bushing 40 must be sealed at two places, the top end 48 of thebushing 40 where it connects with terminal cap 42 and the lower end 50of boshing 40 where it connects with tank cover 44 through opening 52.O-ring 46 is an optional component that can be included between terminalcap 42 and bushing 40 in certain embodiments. The O-ring 46 canaccommodate differences in coefficients of expansion and contractionbetween the metal terminal cap 42 and the non-metallic bushing 40 toreduce or eliminate stresses between the materials.

It was previously believed in this field that a polymer such as an epoxyresin would be incapable of achieving a seal of adequate strength neededfor the capacitor, which is typically expected to have a life of 30years. For example, such polymers may be incapable of withstanding thestresses and weather conditions to which capacitors are typicallysubjected. Furthermore, it was believed that polymers could notwithstand prolonged exposure to the aromatic components of thedielectric fluid within the capacitor.

In accordance with the present disclosure, certain epoxy resincompositions have been identified as unexpectedly providing performancecharacteristics necessary for sealing capacitors. In particular, epoxyresin compositions comprising a curing agent and either a phenol novolacepoxy, a bisphenol A epoxy, or a combination of the two epoxies havebeen found to provide a seal with unexpectedly favorable characteristicswhen joining metallic and non-metallic components of a capacitor. Thecuring agent of the epoxy resin composition can be a hardener, acatalyst, or a combination of a hardener and a catalyst. Examplehardeners include, but are not limited to, amine-containixrg hardenerssuch cyanamide and dicyandiamide. Examples of commercially availableepoxy resin compositions having the foregoing components and producingseals with favorable characteristics include Loctite E-214 HP epoxy,Masterbond Sup 10 ITT epoxy, Pemiabond ES569 epoxy, and Permabond ES550epoxy.

FIG. 4 illustrates an example method 400 for using one of the disclosedepoxy resin compositions in the manufacturing of a sealed capacitor.Referring to example method 400, in step 405, the components of thecapacitor 19 shown in FIG. 3 can be cleaned to remove any contaminants.While not required in every embodiment, removing contaminants from thesurfaces to which the epoxy resin composition is to be applied canimprove the performance of the seal. Processes and cleaners for removingcontaminants from metallic and non-metallic surfaces are well known tothose in the field. However, it should be readily understood that step405 may be unnecessary if, for example, there are no contaminantspresent on the components at the beginning of the manufacturing stage.

In step 410 of example method 400, an epoxy resin composition, such asone of the compositions disclosed herein, is applied to the top end 48and the lower end 50 of the bushing 40. In step 415, the O-ring 46 andthe terminal cap 42 are placed on the top end 48 of the bushing 40. Asindicated previously, certain embodiments may not include the O-ring 46.In step 420, the hushing 40 is inserted into opening 52 in tank-cover44. For certain capacitors such as capacitor 19 shown in FIGS. 1-3,steps 405 through 420 are repeated in step 425 for a second bushing thatis inserted into the second opening 52 in tank cover 44. In alternateembodiments, a capacitor may have more than 2 bushings requiring thatsteps 405 through 420 be repeated more than once. In yet anotheralternative embodiment, a capacitor may have only a single bushing suchthat steps 405 through 420 would not need to be repeated.

Once the pair of bushings is inserted into the tank cover 44, in step430 the epoxy resin composition is cured. While the curing step can beaccomplished through a variety of means, one typical method is byheating of the epoxy resin composition to a predetermined temperature.Heating the epoxy resin composition can be performed through a varietyof means including convection heating, infrared heating, inductionheating, and heating by irradiation. When curing using heat, the curingstep typically requires heating the epoxy resin composition to atemperature between 80° C. and 160° C. Certain epoxy resin compositionsrequire that the composition be held at a temperature between 80° C. and160° C. for about 30 minutes to about 120 minutes. In other embodiments,even longer periods of heating are required for curing.

In step 435, the internal components of the capacitor such as thecapacitor windings 10, the taps 17 and 18, and the leads (not shown) areplaced inside the casing 20, In step 440, the leads are connected to theterminal caps 42. Lastly, in step 445, the tank cover 44 with theattached bushings 40 is sealed to the easing 20. Although notillustrated in exemplary method 400, those in the field will appreciatethat the dielectric fluid is typically added to the capacitor through anopening or fill valve after the tank cover 44 with the attached bushings40 is sealed to die casing 20.

Method 400 is only one example of a process for manufacturing acapacitor in accordance with the current disclosure. Those of skill inthe field will recognize that certain of the steps in example method 400may be omitted or revised without diverging from the scope of thecurrent disclosure. For instance, with respect to steps 410 and 415,they may he modified such that the epoxy resin composition is insteadapplied to the inside surface of the terminal cap 42 and the inner edgeof the opening 52 in the tank cover 44. In yet another embodiment steps410 and 415 may be modified such that the epoxy resin composition isapplied to the top end 48 and the lower end 50 of the boshing 40 as wellas the inner surface of the terminal cap 42 and the inner edge ofopening 52 in the tank cover 44. In yet another embodiment, steps410-420 and 445 can be modified such that the tank cover 44 is firstattached to the easing 20 followed by steps 410-420.

In yet another embodiment, the epoxy resin composition may be a two-partsystem where the two parts of the composition are combined as part ofthe process of applying and curing the epoxy resin composition. As oneexample of a two-part system, the epoxy resin composition can comprise afirst part that comprises an epoxy and a second part that comprises acuring agent. The first part and the second part of the two part systemcan be combined immediately prior to applying the composition to thebushing 40 and/or the inner surface of the terminal cap 42 and the inneredge of the opening 52.

In yet another alternative embodiment, the two-part system can becombined when the bushing 40 is brought into contact with the terminalcap 42 and the edge of the opening 52 in the tank cover 44. For example,a first part of the two-part system can be applied to the top end 48 andthe lower end 50 of the bushing 40. A second part of the two-part systemcan be applied to the inner surface of the terminal cap 42 and the inneredge of the opening 52 in tank cover 44. When the bushing 40 is broughtinto contact with the inner surface of the terminal cap 42 and the inneredge of the opening 52, the first part and the second part of thetwo-part system are combined and cured. The first part can be the epoxyand the second part can be the curing agent. Alternatively, the firstpart can be curing agent and the second part can be the epoxy. These andother variations of example method 400 will be understood to those ofskill in the field.

The following tables provide test data for examples of variouscommercially available epoxy resin compositions that, were tested forpotential use in a capacitor application. As the tables below indicate,only certain of the tested epoxy resin compositions exhibited theproperties necessary for use in a capacitor application. Table 1 showslap shear strength in psi for various epoxy resin compositions tested ata high temperature (HI) of 75° C. to 90° C. and a room temperature (RT)of 25° C. In the instances in Table 1 where no data is present notesting was performed.

TABLE 1 Lap shear Lap Shear No. Product Name (HT) (psi) (RT) (psi) 1. 3MDP420 epoxy <800 3220 2. 3M 2216A/B no data 1656 epoxy 3. 3M 2214 859 nodata epoxy 4. Loctite 7387/331 <800 3200 acrylic 5. Loctite E-214 HP5099 3813 epoxy 6. Delo America no data 1244 Delomonpox 6093 epoxy 7.Lord EP-870 no data no data epoxy 8. Masterbond Sup 10HT 3782 3006.92epoxy 9. Masterbond EP21TDCHT no data 2543.88 epoxy 10. CyberbondCybercryl 800 no data 1722.52 acrylic 11. Permabond PT328 190 2580polyurethane 12. Permabond ES578 no data 1898.296 epoxy 13. PermabondES569 2868 3417.24 epoxy 14. Permabond ES550 2931 3952.56 epoxy

As Table 1 indicates, sample numbers 5, 8, 13 and 14 provided the bestlap shear strength at the temperatures at which the testing wasperformed. Common characteristics found in sample numbers 5, 8, 13 and14 include an amine containing hardener and an epoxy resin comprising aphenol novolac epoxy or a bisphenol A epoxy.

Additional test data for the samples showing the most favorablecharacteristics are shown in Table 2 (below) and in FIG. 7. In order toassess comparability of the aromatic dielectric fluid with the curedseal, cured seals were formed from samples 5 and 8 on example apparatuscontaining the aromatic dielectric fluid Edisol VI, a commerciallyavailable dielectric fluid. The apparatus was heated to 75° C. for twoweeks. Table 2 shows the measurements of certain properties of thearomatic dielectric fluid in the apparatus before (A) and after (B) theheating period.

TABLE 2 Dissipation DC Surface D1816 factor Leakage Tension AcidCondition Specification >60 kV <0.0010 <0.10 μA >40  <0.10 mg Clear,dynes/cm KOH/g Clean Loctitie 64 0.0008 0.03 41.8 0.003 Clear, E214HP(A) Clean Loctitie 62 0.0007 0.02 41.6 0.003 Clear, E214HP (B) Clean MS10HT (A) 66 0.001 0.05 40.8 0.002 Clear, Clean MS 10HT (B) 62 0.00110.04 40.9 0.003 Clear, Clean

In particular, the data in Table 2 shows that cured seals formed fromsamples 5 and 8 performed well in that they did not have an adverseeffect on a dielectric fluid that could be used in the capacitor. Forexample, comparing the test samples before the heating period (A) andafter the two week heating period (Bp shows there was relatively littlechange In the properties of the dielectric fluid. The data in Table 2shows the cured seals did not materially affect the electricalproperties of the dielectric fluid such as the breakdown voltage (testedusing ASTM D1816), the dissipation factor (tested using ASTM D924), orcurrent leakage. Techniques for measuring current leakage are generallyknown to those in the field. The data in Table 2 also shows no materialchanges in the measured surface tension, the acidity, or the visibleappearance of the dielectric fluid when comparing data collected beforethe heating period (A) and after the two week heating period (B). Thefigures in the row labeled Specification are typical target values foreach property.

The impact of the aromatic fluid on the hardness of cured seals formedfrom samples 5, 13 and 14 was also evaluated. FIG. 7 shows hardness testdata for samples 5, 13 and 14 throughout 120 days of exposure toaromatic dielectric fluid at 75° C. In particular, FIG. 7 shows that thearomatic dielectric fluid did not have an adverse effect on the hardnessof the cured seals formed from samples 5, 13 and 14 even after 120 daysof exposure to the aromatic dielectric fluid.

Samples 5, 13 and 14 were also subjected to other tests to ensure theywould withstand the harsh environmental conditions to which capacitorsare subjected. Additional tests that the samples withstood included athermal shock test, a salt spray test, a UV test a condensation test,and a helium leak test.

The thermal shock test was performed on assemblies that included acapacitor tank cover with bushings attached using sample 5 from theTable 1. The thermal shock test involved heating the assemblies to 110 °C. and then quickly moving the assemblies to a chamber held at atemperature of −50 ° C. overnight. The assemblies were then warmed in aroom at room temperature and subjected to load testing. There was nostatistical difference in the performance of the assemblies under theload testing when comparing testing results of samples subjected to thetemperature changes with samples that were not subjected to thetemperature changes.

Samples 5, 13 and 14 from Table 1 were applied to a piece of stainlesssteel and subjected to a salt spray test in accordance with ASTM B117for 2000 hours. The samples were examined after the 2000 hours ofexposure to salt spray and showed no evidence of delamination, noevidence of creepage from scrap, and no change is the pencil hardness ofthe cured seal.

Samples 5, 13 and 14 from Table 1 were also applied to a piece ofstainless steel and subjected to ultraviolet light exposure inaccordance with ASTM D4587 for 2000 hours. Examination of the samplesafter the 2000 hours of exposure to ultraviolet light showed a change incolor but no change in the pencil hardness of the samples.

Samples 5, 13 and 14 from Table 1 were also applied to a piece ofstainless steel and subjected to condensation testing in accordance withASTM D4586-99 for 2000 hours. Examination of the samples after the 2000hours of exposure to condensation showed no evidence of delaniinationand no change in the pencil hardness of the cured seal.

Lastly, example capacitor assemblies made with cured seals from epoxyresin samples 5, 13 and 14 from Table 1 were subjected to a helium leaktest. The helium leak test demonstrated that a hermetic seal wasmaintained with each sample.

Referring now to FIG. 5, a representation is shown of an adhesive 505bonding a ceramic material 501 to stainless steel 509. Therepresentation shown in FIG. 5 provides a general illustration of how anadhesive 505, such as the epoxy resin compositions disclosed herein, canbe used to join dissimilar materials such as a ceramic material 501 anda metallic material such as stainless steel 509. As illustrated in FIG.5, a ceramic material 501 will often have an outer glaze layer 503 towhich the epoxy resin composition is applied. On the opposing face ofthe joint, the metallic material 509 typically has an outer oxidationlayer 507 caused by exposing the metallic material to moisture typicallypresent in the atmosphere. As shown in the generalization in FIG. 5, theepoxy resin compositions disclosed herein can be used to join a varietyof dissimilar materials and are not limited to the capacitor exampledescribed, in connection with FIGS. 1 through 4. As explained above, theepoxy resin compositions disclosed herein, can be used to join a varietyof dissimilar materials subjected to stress and harsh environmentalconditions such as fuses, switchgear, regulators and transformers.

FIG. 6 provides an example illustration of the metallic material portionof the joint in greater detail. In particular, FIG. 6 shows in greaterdetail the layers that can be found in oxidation layer 507 of FIG. 5. Atthe base of the metallic layer is the bulk stainless steel 609. litebulk stainless steel layer 609 comprises primarily metallic molecules.Moving towards the outer layers of the steel, the next layer is thesegregation layer 611. The segregation layer 611 is the interfacebetween the bulk stainless steel 609 and the metal oxide layer 613. Themetal oxide layer 613 comprises primarily metal oxide molecules.Continuing to move outward from the steel, the next layer is thehydroxide and moisture layer 615. On the right-hand side of FIG. 6,layer 615 is shown in greater detail as having a distinct hydroxidelayer and a distinct hydrated water layer. Finally, layer 617 of FIG. 6represents oils and contaminants that may be present on the outermostlayer of the metallic material. Preferably, the oils and contaminantsare removed prior to application of the epoxy resin composition so as tomaximize the interaction of the epoxy groups with the hydroxidemoieties. Those of skill in this field will appreciate the illustrationof FIG. 6 is an example and metallic materials other than steel or steelsubjected to different environmental conditions may have differentoxidation layers than those illustrated in FIG. 6.

On the side of the joint opposite the steel 509 in the example shown inFIG. 5, the adhesive 505 (epoxy resin) is bonded to a non-metallicmaterial such as ceramic 501, In the example shown in FIG. 5, theceramic 501 has an outer glaze layer 503 that typically comprises metaloxides. Similar to the bonding that occurs between the epoxy resin andthe metallic layer as described in connection with FIG. 6, the epoxyresin interacts with the metal oxides present in the glaze layer 503 toform a chemical bond. However, in alternate embodiments, the adhesive505 can bond to ceramics with glaze layers made of other materials orwithout any glaze layer. Although the examples above refer to ceramic501 as the non-metallic material, other example embodiments may useother non-metallic materials as an insulator such as a bushing made ofepoxy.

The epoxy resin compositions disclosed herein are able to provide a sealbetween the dissimilar components of a capacitor that can withstand theharsh environmental conditions to which a capacitor is subjected.Although the example of a capacitor is provided herein, the disclosedepoxy resin compositions can be applied to join dissimilar materials inother types of equipment as well.

Although embodiments described herein are made with reference to exampleembodiments, it should be appreciated by those skilled in the art thatvarious modifications are well within the scope and spirit of thisdisclosure. Those skilled in the art will appreciate that the exampleembodiments described herein are not limited to arty specificallydiscussed application and that the embodiments described herein areillustrative and not restrictive. From the description of the exampleembodiments, equivalents of the elements shown therein will suggestthemselves to those skilled in the art, and ways of constructing otherembodiments using the present disclosure will suggest themselves topractitioners of the art. Therefore, the scope of the exampleembodiments is not limited herein.

What is claimed is:
 1. A capacitor tank comprising: an insulatinghushing comprising substantially glass, ceramic, polymer, or glazedmaterial; a metallic tank cover; a casing attached to the metallic tankcover, the casing to contain a fluid comprising one or more aromaticcompounds; and a cured seal between the insulating bushing and themetallic tank cover, wherein the cured seal comprises an epoxy resincomposition, wherein the epoxy resin composition comprises a curingagent and one or both of a phenol novoiac epoxy and a bisphenol A epoxy,and wherein the cured seal is exposed to the fluid comprising one ormore aromatic compounds when the capacitor tank is completely assembled.2. The capacitor tank of claim 1, wherein the curing agent is anamine-containing hardener.
 3. The capacitor tank of claim 1, wherein thecuring agent is cyanamide or dicyandiamide.
 4. The capacitor tank ofclaim 1, wherein the epoxy resin composition comprises a polymer contentof at least about 50% polymer content.
 5. The capacitor tank of claim 1,wherein the one or more aromatic compounds are selected from the groupconsisting of diaryl ethanes, diaryl methanes, triaryl methanes, triarylethanes, biphenyls, monoaromatics and naphthalenes.
 6. The capacitortank of claim 1, wherein the epoxy resin composition is cured by heatingthe epoxy resin composition to between about 80° C. to about 160° C. andholding the epoxy resin composition between about 80° C. to about 160°C. for about 30 minutes to about 120 minutes, or by induction heatingtor about 1 to about 10 minutes.
 7. The capacitor tank of claim 1,wherein the cured seal is hermetic.
 8. The capacitor tank of claim 1,wherein the cured seal resists breakage after 2000 hours of exposure toone or more of salt spray, ultraviolet light, and 100% relativehumidity.
 9. The capacitor tank of claim 1, wherein the hardness of theseal decreases less than 2% after 120 days in the fluid comprising oneor more aromatic compounds.
 10. The capacitor tank of claim 1, whereinthe epoxy resin composition comprises a two-part system wherein a firstpart comprises an epoxy and a second part comprises a curing agent. 11.A capacitor tank comprising: an insulating bushing; a metallic tankcover; a casing attached to the metallic tank cover, the casing tocontain a dielectric fluid; and a cured seal between the insulatingbushing and the metallic tank cover, wherein the cured seal comprises anepoxy resin composition, wherein the epoxy resin composition comprises acuring agent and one or both of a phenol novolae epoxy and a bisphenol Aepoxy, and wherein the cured seal is exposed to the dielectric fluidwhen the capacitor tank is completely assembled.
 12. The capacitor tankof claim 11, wherein the curing agent is an amine-containing hardener.13. The capacitor tank of claim 11, wherein the curing agent iscyanamide or dicyandiamide.
 14. The capacitor tank of claim 11, whereinthe epoxy resin composition comprises a polymer content of at leastabout 50% polymer content.
 15. The capacitor tank of claim 11, whereinthe dielectric fluid comprises one or more aromatic compounds that areselected from the group consisting of diaryl ethanes, diaryl methanes,triaryl methanes, triaryl ethanes, biphenyls, monoaromatics andnaphthalenes.
 16. The capacitor tank of claim 11, wherein the epoxyresin composition is cured by heating the epoxy resin composition tobetween about 80° C. to about 160° C. and holding the epoxy resincomposition between about 80° C. to about 160° C. for about 30 minutesto about 120 minutes, or by induction heating for about 1 to about 10minutes.
 17. The capacitor tank of claim 11, wherein the cured seal ishermetic.
 18. The capacitor tank of claim 11, wherein the cured sealresists breakage after 2000 hours of exposure to one or more of saltspray, ultraviolet light, and 100% relative humidity.
 19. The capacitortank of claim 11, wherein the hardness of the seal decreases less than2% after 120 days in the dielectric fluid.
 20. The capacitor tank ofclaim 11, wherein the epoxy resin composition, comprises a two-partsystem wherein a first part comprises an epoxy and a second partcomprises a curing agent.